Laser technology is well suited for cutting, e.g. cloth, plastic sheets, plate or fibre particle boards, since, inter alia, the cutting laser beam can be made very narrow and energy-intensive, whereby material waste will be very small.
For such cutting processing, it is suitable to arrange a work table for the material. A first slide can be displaceably arranged along the table and extend transverse the table. A second slide can be displaceably arranged on the first slide for displacement along the first slide, i.e. across the table. By controlled displacement of the two slides the second slide can be caused to find an arbitrary point on the table. Such controlled displacement can be provided by conventional technology with the aid of numerical control, i.e. the driving means of the slides are controlled with the aid of a programmed computer.
It is already known in plants of the kind mentioned in the introduction to mount the laser unit directly on the second slide, it thus being achieved that the beam can be easily enclosed along the short distance between the unit and the material to be cut. The exposed beam between the casing and material is so short that an operator can hardly come against, and be injured by the beam.
Since the laser unit can have a mass of about 400 kg, and since in plants of the kind in question it is desirable to have a cutting speed which is as high as possible in the plane of the table, it will be understood that the plant is subjected to large stresses due to the mass of the laser unit when the direction and rate of travel of the second slide are changed. For reasons of precision and strength, such a known plant must therefore be implemented very robustly and it will therefore be very expensive. The cutting speed can hardly be made larger than some few m/min even so.
The laser unit has therefore been placed stationary relative the table, the "weightless" laser beam being deflected instead to desired points on the table with the aid of deflection mirrors, the beam path then being enclosed in a telescopic-type tube system, cf SE 347 680. The tube system serves the purpose of preventing the operator from being injured by the laser beam, it thus preventing direct contact with the beam and constitutes a dazzle shield so that eye injuries are avoided. Furthermore, the system can serve to prevent dirtying the mirrors which are placed in the tube system.
Telescopic tube systems have been found to be substantially unusable, at least with relatively large cutting table surfaces, e.g. 2.times.3 m, and cutting speeds in the order of magnitude of 1 m/s.
Among the reasons for this is that it is very difficult to get a telescope sufficiently rigid when fully extended, since only the outer sections of the telescope can be supported. It is indeed possible to utilize telescopic tube sections for the telescope which have very great lengths relative their diameter and are also provided with long guides. However, this results in special difficulties with the second telescopic tube in the direction of the ray path, since it must carry a deflection mirror at the connection with the first telescopic tube. This mirror will then be outside the edge of the table by a telescopic section length. In order to be able to operate this mirror without vibration, which is particularly difficult since the sections of the first telescopic tube tend to hook into each other, the second slide would need to be provided with a support carrying the mirror in question at a distance from the table corresponding to a telescopic section length. In turn, this results in further weight problems.
Furthermore, the varying and periodical friction occurring in telescopic tubes would make the use of numerical control impossible, at least for a plant working at such a high speed, since every frictional resistance must be compensated for in the calculation of the control pulses to the driving means of the slide.
Another disadvantage with a telescopic tube system is that the air therein is pumped in and out, and dust would be deposited onto and fused into the mirrors.